High Level Concepts

Question 1

First Class Functions

Answer 1

Functions are treated as variables

Question 2

Single Threaded

Answer 2

One command is processed at a time

Question 3

Event loop

Answer 3

Takes long running tasks, executes them in the background, and puts them back in the main thread once they are completed

Question 4

Compilation

Answer 4

Entire codebase is converted into machine code at once, and written to a binary file that can be executed by a computer

Question 5

Interpretation

Answer 5

Interpreter runs through the source code and executes it line by line

Question 6

Just-in-time Compilation

Answer 6

Entire code is converted into machine code at once, then executed immediately

Question 7

Web API’s

Answer 7

Functionalities provided to the engine, available on the window object. DOM, Times, Fetch…

Question 8

Top-level code

Answer 8

All code outside of functions

Question 9

Global Execution Context

Answer 9

Default execution context stated when a file is loaded in the browser. All top-level code is executed here

Question 10

Execution context

Answer 10

The environment in which the javascript code is executed

Question 11

Call Stack

Answer 11

Place where execution contexts get stacked on top of each other, to keep track of where we are in the execution

Question 12

What Makes Up An Execution Context

Answer 12

1. Variable environment
2. Scope Chain
3. “this” keyword

Question 13

Lexical Scoping

Answer 13

Defines how variable names are resolved in nested functions

Question 14

Scope

Answer 14

The accessibility or visibility of variables

Question 15

3 Types of Scope

Answer 15

Global, function and block

Question 16

Scope Chain

Answer 16

Used to resolve the value of variable names in javascript.

Question 17

Hoisting

Answer 17

Makes some types of variables accessible/usable in the code before they are declared

Question 18

Types of variables that are hoisted

Answer 18

function declarations, variables declared with var

Question 19

Temporal Dead Zone

Answer 19

Region of scope where a variable is defined but cannot be used

Question 20

Types of variables that are not hoisted

Answer 20

let and const variables, arrow expressions

Question 21

This keyword

Answer 21

Special variable created in every execution context. Takes the value of the owner.

Question 22

Primitive types

Answer 22

Number, string, boolean, null, undefined, symbol, bigint

Question 23

Remainder operator

Answer 23

Returns the remainder left over when one operand is divided by a second operand

Question 24

References the DOM object that dispatched an event

Answer 24

Target

Question 25

Statement used to skip an iteration in a loop

Answer 25

Continue

Question 26

What is null

Answer 26

The absence of a value

Question 27

What is eval()

Answer 27

The eval() function evaluates JavaScript code represented as a string.

Question 28

Defining default function parameters

Answer 28

function myFucntion(defaultValue = something) {}

Question 29

Is JavaScript able to pass by reference

Answer 29

No, only by value

Question 30

Higher Order Function

Answer 30

A function that receives another function as an argument

A function that returns a new function

Question 31

Function.prototype.call()

Answer 31

Calls a function with a given this value and arguments provided individually.

Question 32

Partial Application

Answer 32

Preset function parameters before being called

Question 33

Function.prototype.bind()

Answer 33

Creates a new function that, when called, has its this keyword set to the provided value, with a given sequence of arguments preceding any provided when the new function is called.

Question 34

Closure

Answer 34

The closed-over variable environment of the execution context in which a function was created, even after that execution context is gone.

Question 35

Promise

Answer 35

An object that is used as a placeholder for the future result of an asynchronous operation.